Lens apparatus for projection

ABSTRACT

A lens apparatus for projection includes a plurality of lenses on an optical axis. A shading plate  11  for covering the peripheral portion of the lens to block off light entering the peripheral portion is provided as a single member on the optical axis with the lenses to omit an inking process. In addition, the shading plate  11  is integrally provided with a contrast compensating plate  13  for compensating a projected image, so that it is not required to provide any portions for supporting the contrast compensating plate  13 . Moreover, a shading wall  23  for blocking off light leaking out of the peripheral portion of the lens is provided on the peripheral portion of the shading plate  11 . Thus, it is possible to provide a lens apparatus for projection, which has a simple structure and which can be easily assembled to reduce the producing costs.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of Ser. No. 09/690,808filed Oct. 18, 2000, now U.S. Pat. No. 6,552,859.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a lens apparatus forprojection wherein the adjustment of contrast and shading means areimproved.

2. Description of the Prior Art

In recent years, television projectors are widely utilized as displaysfor displaying images received from television broadcasting, as well asimages outputted from electronic image apparatuses, such as VTRs.Although lens apparatuses for projection for use in such projectors havea very great power, it is naturally required that the lens apparatuseshave various small aberrations to realize good optical characteristics.

An example of such a lens apparatus for projection is shown in FIG. 2.This lens apparatus for projection 1 comprises a negative first lensgroup 2, a positive second lens group 3, a positive third lens group 4having the strongest power of component lenses, a positive fourth lensgroup 5, a positive fifth lens group 6, a negative sixth lens group 7,and a negative field curvature correction unit 8 for correcting almostall of the curvature of field of the lens system, which are arranged inthat order from the side of a screen. In this example, each of the firstthrough sixth lens groups is a single lens. This lens apparatus forprojection 1 is integrated with a cathode-ray tube (not shown) to beused.

The field curvature correction unit 8 comprises a left first lensportion 8A, a right second lens portion 8B, a cooling liquid 8 c, whichis filled therebetween for fulfilling lens functions, and an inkedportion 8D which is provided on the left side face of the first lensportion 8A. The inked portion 8D is applied on the periphery of the leftside face of the first lens portion 8A for removing undesired light,such as scattered light, which is incident on the periphery of the lens,to prevent light from diffusing.

In accordance with colors of RGB, three lens apparatuses for projectionare provided in parallel. These three lens apparatuses for projectionfor colors of RGB are usually arranged laterally.

By the way, in a system for projecting light from three light sourcesfor RGB, which are laterally arranged, to project an image, there is thefollowing disadvantage. That is, since the central light source isprovided at a position, at which its optical axis is perpendicular tothe surface of the screen, to perpendicularly irradiate the surface ofthe screen with light, the difference in contrast does not appear on theirradiated surface, but the difference in contrast appears by the lightsources which are provided on the right and left sides. That is, lightemitted from the light source provided on the left side with respect tothe screen is bright on the surface of the screen on the left side whichis near the light source, and dark on the surface of the screen on theright side which is distant from the light source, whereas light emittedfrom the light source provided on the right side with respect to thescreen is bright on the surface of the screen on the right side which isnear the light source, and dark on the surface of the screen on the leftside which is distant from the light source.

In order to solve this disadvantage, a contrast adjusting plate (notshown) is provided on the left side of the first lens portion 8A of thefield curvature correction unit 8. This contrast adjusting platecomprises a single member, such as an elongated plate, and is arrangedon the left side of the first lens portion 8A. Since the contrastadjusting plate must be accurately positioned, a portion for supportingthe contrast adjusting plate is provided.

However, the operation for applying the above described inked portion 8Don the periphery of the left side face of the first lens portion 8A cannot be easily carried out, and one step of applying operation is addedto the assembly operation.

In addition, the lens apparatus for projection must be provided with theportion for supporting the contrast adjusting plate, so that thestructure of the lens apparatus for projection is complicated.

As a result, there is a problem in that the cost of producing the lensapparatus for projection is increased.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to eliminate theaforementioned problems and to provide a lens apparatus for projection,which has a simple structure and which can be easily assembled to reducethe producing costs.

In order to accomplish the aforementioned and other objects, accordingto one aspect of the present invention, a lens apparatus for projectioncomprises: a lens or two or more lenses provided on an optical axis; anda shading plate, provided as a single member on the optical axis withthe lens or one of the lenses, for covering a peripheral portion of thelens or the one of the lenses to block off light entering the peripheralportion.

With this construction, since the shading plate is provided as a singlemember, it is possible to omit an inking process, which takes time.

The lens apparatus for projection may further comprise a contrastcompensating plate for compensating contrast of a projected image, thecontrast compensating plate being integrated with the shading plate.

With this construction, since the contrast compensating plate isintegrated with the shading plate, it is not required to provide anyportions for supporting the contrast compensating plate, so that it ispossible to reduce the number of parts. Thus, it is possible to reducethe costs of producing the lens apparatus for projection since it isalso possible to omit the inking process which takes time.

The lens apparatus for projection may further comprise a shading wallfor blocking off light leaking out of the peripheral portion of the lensor the one of the lenses, the shading wall being formed on a peripheralportion of the shading plate by extending or bending the peripheralportion of the shading plate.

With this construction, the shading wall can surely block off light,such as scattered light, which leaks out of the periphery of the lens.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of thepreferred embodiments of the invention. However, the drawings are notintended to imply limitation of the invention to a specific embodiment,but are for explanation and understanding only.

In the drawings:

FIG. 1 is a sectional view of a shading plate of the first preferredembodiment of a lens apparatus for projection according to the presentinvention;

FIG. 2 is a schematic sectional view showing the construction of a lensapparatus for projection;

FIG. 3 is a plan view of a shading plate for red;

FIG. 4 is a plan view of an oblique plate portion for blue;

FIG. 5 is a sectional view of an engaged recessed portion of a shadingplate;

FIG. 6 is a sectional view of a first modified example of a shadingplate;

FIG. 7 is a plan view of a second modified example of a shading plate;

FIG. 8 is an enlarged view of a principal part of the second modifiedexample;

FIG. 9 is a sectional view of a third example of a shading plate; and

FIG. 10 is a sectional view of a fourth example of a shading plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, a preferred embodiment of alens apparatus for projection according to the present invention will bedescribed below. Since the whole construction of a lens apparatus forprojection in this preferred embodiment is substantially the same asthat of the above described lens apparatus for projection, the samereference numbers are given to the same members, and the descriptionthereof is omitted.

In this preferred embodiment, a first lens portion 10 corresponding tothe first lens portion 8A of the conventional field curvature correctionunit 8 has a flange portion 10A. That is, the flange portion 10A isprovided so as to continuously extend around a concave side portion 10Bwhich contributes to the refraction of light.

The lens apparatus for projection in this preferred embodiment ischaracterized in that a shading plate 11 is provided in place of theconventional inked portion 8D and contrast adjusting plate. This shadingplate 11 is shown in FIGS. 1, 3, 4 and 5. Furthermore, FIG. 3 is a planview of a shading plate 11R for red, and FIG. 4 is a plan view of ashading plate 11B for blue.

The shading plate 11 (including both of the shading plate 11R for redand the shading plate 11B for blue) mainly comprises a ring portion 12and a plate portion 13.

The ring portion 12 comprises an annular flat plate portion 14 and aconical oblique plate portion 15. The annular flat plate portion 14 is amember for contacting the flange portion 10A of the first lens portion10 to support the shading plate 11 on the side of the first lens portion10. The inside diameter of the annular flat plate portion 14 is set tobe substantially equal to the inside diameter of the peripheral portionof the concave side portion 10B. Thus, the outside diameter of aboundary portion between the conical oblique plate portion 15 and theannular flat plate portion 14 is substantially equal to the insidediameter of the peripheral portion of the concave side portion 10B. As aresult, when the ring portion 12 is fitted into the first lens portion10, the ring portion 12 is precisely positioned without being rattled(in a direction perpendicular to the optical axis).

The annular flat plate portion 14 is provided with engaged recessedportions 17 at opposite two positions. The flange portion 10A of thefirst lens portion 10 is provided with engaging protruding portions 18at positions facing the engaged recessed portions 17. By fitting theengaging protruding portions 18 into the engaged recessed portions 17,the shading plate 11 is positioned in rotational directions with respectto the first lens portion 10.

The conical oblique plate portion 15 is a member for covering the insideof the periphery of the concave side portion 10B of the first lensportion 10 to block off undesired light, such as scattered light. Thisconical oblique plate portion 15 is formed so as to conically projectalong the inside of the concave side portion 10B of the first lensportion 10 from the inner edge of the annular flat plate portion 14. Theconical oblique plate portion 15 covers the periphery of the first lensportion 10 to block off undesired light, such as. scattered light.

The plate portion 13 is a contrast compensating plate, and is integrallyformed with the ring portion 12. This plate portion 13 is provided onthe tip side of the conical oblique plate portion 15 (on the right sidein FIG. 1).

As shown in FIG. 3, the shading plate 11R for red is provided with asingle plate portion 13R on the slightly right side from the center ofthe ring portion 12. This plate portion 13R comprises an elongated platemember having a constant width.

As shown in FIG. 4, the shading plate 11B for blue is provided with asingle plate portion 13B on the slightly left side from the center ofthe ring portion 12. This plate portion 13B comprises an elongated platemember having a constant width similar to the above described plateportion 13R.

The shading plate 11 with the above described construction is combinedwith the first lens group 2 through the sixth lens group 7 and the fieldcurvature correction unit 8 when the lens groups 2 through 7 and theunit 8 are assembled. Specifically, the conical oblique plate portion 15of the shading plate 11 is inserted into the concave side portion 10B ofthe first lens portion 10, and the engaged recessed portions 17 of theshading plate 11 are fitted into the engaging protruding portions 18 ofthe first lens portion 10. Thus, the shading plate 11 can be easily andsurely positioned in vertical and lateral directions (directionsperpendicular to the optical axis) and rotational directions withrespect to the first lens portion 10. Moreover, the plate portion 13serving as a contrast compensating plate is also simultaneouslypositioned.

If the shading portion 11 is thus mounted on the first lens portion 10,it is possible to easily assemble the lens apparatus for projection, andit is not required to provide any portions for supporting the shadingplate 11 and the plate portion 13, so that it is possible to simplifythe structure of the lens apparatus for projection.

As a result, it is possible to reduce the cost of producing the lensapparatus for projection.

MODIFIED EXAMPLES

(1) While the outer peripheral portion of the shading plate 11 has beenthe flat plate portion in the above described preferred embodiment, ashading wall 21 may be provided as shown in FIG. 6. This shading wall 21is formed by bending the outer peripheral portion of the shading plate11 toward the light source. By this shading wall 21, it is possible tosurely block off undesired light, such as scattered light, which entersthe peripheral portion of the first lens portion 10.

The shading wall 21 may be formed so as to extend radially outsidewithout bending the outer peripheral portion of the shading plate 11toward the light source. Alternatively, the shading wall 21 may beformed by bending the outer peripheral portion of the shading plate 11in the opposite direction to the light source. Also in these cases, itis possible to surely block off undesired light, such as scatteredlight, which enters the peripheral portion of the first lens portion 10.

(2) While the engaged recessed portion 17 has been provided as means forpreventing the rotation of the shading plate 11 in the above describedpreferred embodiment, such means for preventing the rotation of theshading plate 11 may be formed as shown in FIGS. 7 and 8. That is, apart of the annular flat plate portion 14 may be extended radiallyoutside to form a fan-shaped portion 22, and a shading wall 23 may beformed by bending the edge portion of the fan-shaped portion 22 towardthe light source. Moreover, a V-shaped notch 24 may be formed in theedge portion of the shading wall 23 to engage a V-shaped protrusion 25of the apparatus body. Thus, the shading plate 11 can be easily andsurely positioned in vertical and lateral directions (directionsperpendicular to the optical axis) and rotational directions withrespect to the first lens portion 10. The notch 24 and the protrusion 25may have any shape, such as semicircle, trapezoid, quadrangle or combteeth, as long as the notch 24 engages the protrusion 25 to position theshading plate 11 in rotational directions.

(3) While the shading plate 11 has been integrally formed with the plateportion 13 in the above described preferred embodiment, the plateportion 13 may be omitted as shown in FIG. 9 to omit the inking processwhich takes time.

(4) While the plate portion 13 has been provided on the tip side of theconical oblique plate portion. 15 of the shading plate 11 in the abovedescribed preferred embodiment, the plate portion 13 may be provided onthe base end side as shown in FIG. 10. Also in this case, it is possibleto obtain the same operation and effects as those in the above describedpreferred embodiment.

(5) While the plate portion 13R of the shading plate 11R for red hasbeen formed as shown in FIG. 3 and the plate portion 13B of the shadingplate 11B for blue has been formed as shown in FIG. 4 in the abovedescribed preferred embodiment, the plate portions 13R and 13B may bedesigned so as to have any one of various shapes if necessary. That is,since the degree of contrast varies in accordance with variousconditions, such as the size of lenses and the difference in refractiveindex, the position, number and shape of the plate portions 13R and 13Bare suitably designed in accordance with the respective conditions.

As describe above, according to the present invention, the shading platefor covering the peripheral portion of the lens to block off lightentering the peripheral portion is provided as an independent singlemember readily positioned during assembly by mating portions of the lensand shading plate, so that it is possible to omit the inking processwhich takes time.

In addition, since the shading plate is integrally formed with thecontrast compensating plate for compensating contrast of the projectedimage, it is not required to provide any portions for supporting thecontrast compensating plate, so that it is possible to reduce the numberof parts. Thus, it is possible to reduce the costs of producing the lensapparatus for projection since it is also possible to omit the inkingprocess which takes time.

Moreover, since the shading wall for blocking off light leading out ofthe periphery of the lens is provided on the periphery of the shadingplate by extending or bending the periphery of the shading plate, theshading wall can surely block off light, such as scattered light, whichleaks out of the periphery of the lens.

While the present invention has been disclosed in terms of the preferredembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. A lens apparatus for projection of an image, thelens apparatus comprising: at least one lens having an optical axis; andan annular shading plate, provided as a single member on said opticalaxis, for covering a peripheral portion of said at least one lens toblock off scattered light which is incident on said peripheral portion;wherein said at least one lens has a curved surface, and said shadingplate has a conical portion for fitting a peripheral curved portion ofthe curved surface to block undesired light.
 2. A lens apparatus forprojection of an image, the lens apparatus comprising: at least one lenshaving an optical axis; and an annular shading plate, provided as asingle member on said optical axis, for covering a peripheral portion ofsaid at least one lens to block off scattered light which is incident onsaid peripheral portion; wherein said at least one lens has a concaveportion surrounded by a flange portion; and said shading plate has anannular flat plate portion for contacting the lens flange portion andhas a conical oblique portion for fitting into a peripheral portion ofthe lens concave portion.
 3. A lens apparatus for projection of animage, the lens apparatus comprising: at least one lens having anoptical axis; and an annular shading plate provided as a single memberon said optical axis for covering a peripheral portion of said at leastone lens to block off scattered light which is incident on saidperipheral portion; wherein said at least one lens and said annularshading plate have mating portions positioning said annular shadingplate relative to said at least one lens in directions perpendicular tothe optical axis.
 4. A lens apparatus according to claim 3 whereinmating portions also position said shading plate relative to said atleast one lens in a rotational direction about said optical axis.